<template>
  <button @click="show = !show">显示/隐藏</button>
  <transition name="fade" class="dv">
    <div v-if="show">Hello,Vue3</div>
  </transition>
</template>

<script setup>
import { ref } from 'vue';

let show = ref(false)
</script>

<style>
.dv{
    margin-top: 20px;
    padding: 30px;
    background-color: aqua;
    color:red;
}
.fade-enter-active,.fade-leave-active{
    transition: opacity 5s ease;
}
.fade-enter-from,
.fade-leave-to{
    opacity: 0;
}
</style>